Tip assembly for a carbon fiber implantable lead

ABSTRACT

A termination for a carbon fiber implantable lead. A tip assembly includes an electrode to which carbon fiber tips are cemented with a conductive adhesive. An outer housing cooperatively interacts with the electrode to mechanically secure the carbon fiber bundle sheathing to the electrode, and also to establish good electrical contact between the carbon fiber bundles and the electrode.

REFERENCE TO RELATED APPLICATION

The subject matter of this application is related to that of U.S. Pat.No. 4,198,991 entitled "Cardiac Pacer Lead" and also to that of my U.S.patent application entitled "Terminal Assembly for a Carbon FiberImplantable Lead", filed on even data herewith. The patent andapplication are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention is in the field of implantable leads, moreparticularly, terminations for carbon fiber implantable leads.

There have been increasing applications in recent years for implantableelectrical leads for coupling electrical signals to and from or betweenvarious points in human or animal bodies. The incorporated referencepatent describes one such application, that is, cardiac pacing by meansof an implantable stimulator. As particularly pointed out in thatreference, such implantable leads are typically subject to continuousflexing which may result from heartbeat, breathing or other bodymovements. Consequently, the leads are designed to be both pliant andfatigue-resistant.

The incorporated reference patent discloses a carbon fiber lead which isparticularly well-suited for cardiac pacing and which is highly pliantand fatigue-resistant.

One of the difficulties with implantable carbon fiber leads in the priorart is the coupling of a termination assembly to the carbon fiber leadsat both the tip end (which is implantable within a patient), and theterminal end (which is the end to be coupled to either sensorinstrumentation or signal generating instrumentation). In typical priorart carbon fiber leads, particularly those having bundles of carbonfibers, or yarn, sheathed in tetrafluoroethylene, there has proven to bea substantial problem due to the inability to maintain a long lifemechanical coupling between the terminations and the sheathing material.

It is an object of the present invention to provide an improved tipassembly for carbon fiber implantable leads.

It is yet another object to provide an improved tip assembly for acarbon fiber implantable lead which provides good electrical contactbetween an electrode tip and the internal carbon fiber bundles, whilemaintaining good mechanical coupling between the tip assembly and thelead.

SUMMARY OF THE INVENTION

Briefly, the present invention includes a tip assembly for animplantable carbon fiber lead having an outer cover positioned about astylet tube and one or more carbon fiber bundles. Each carbon fiberbundle has an insulating outer sheath (for example, made of afluorocarbon material such as polytetrafluoroethylene, PTFE) and has anexposed carbon fiber tip at one end. The tip assembly includes anelectrode having a tip portion at one end and a contact portion, a neckportion interconnecting the tip and contact portions along a centralaxis, and a post portion extending along the central axis at its otherend. The neck portion has a relatively small cross-sectional areacompared to the adjacent portions of the tip and contact portions. Thecontact portion includes a plurality of substantially planar lateralcontact surfaces.

The exposed tips of the carbon fiber bundles and the stylet tube extendto respective axes of the contact surfaces, and extend beyond to theneck portion of the electrode.

An electrically conductive adhesive cements a portion of each of theexposed tips of the carbon fiber bundles to an associated one of thecontact surfaces.

A hollow, cylindrical electrically conductive electrode housing member,having a lip at one end, is positioned about the post portion, contactportion and region of the neck of the electrode. The portion of thehousing member which overlies the neck portion is crimped in a mannermechanically securing (and electrically coupling) the exposed tipsbetween the housing and electrode in the region of the crimp. Inaddition, the housing crimp mechanically secures the fiber bundlesheathing between the housing lip and the post portion of the electrode.In some forms of the invention, the housing interior surfacefrictionally engaging two or more of the regions of the contact portionbetween, or at the intersections of, the contact surfaces.

With this configuration, the carbon fiber lead is provided with anelectrode termination which is securely coupled to the carbon fiber leadin a manner minimizing slipping and dislodging of the termination fromthe lead, thereby providing a relatively long life assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects of this invention, the various featuresthereof, as well as the invention itself, may be more fully understoodfrom the following description, when read together with the accompanyingdrawings in which:

FIG. 1 shows an implantable carbon fiber lead embodying the presentinvention;

FIG. 2 shows a cutaway view of the tip assembly of the lead of FIG. 1;

FIG. 3 shows the electrode of the tip assembly of FIGS. 1 and 2;

FIG. 4 shows a section of the electrode of FIG. 3 along lines 4--4;

FIG. 5 shows the electrode housing of the tip assembly of FIGS. 1 and 2;

FIG. 6 shows a cutaway view of the terminal assembly of the lead of FIG.1;

FIG. 7 shows, in section, the terminal member of the terminal assemblyof FIGS. 1 and 6;

FIG. 8 shows a section of the terminal member of FIG. 7 along lines8--8;

FIG. 9 shows a cutaway view of the housing member of the terminalassembly of FIGS. 1 and 6; and

FIG. 10 shows a cutaway view of the guide member of the terminalassembly of FIGS. 1 and 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1-10 show an implantable carbon fiber lead 10 embodying thepresent invention. Lead 10 generally includes an outer cover 12 (e.g.made of a suitable material such as polyurethane or silastic) whichencloses a stylet tube 14 and two carbon fiber bundles 16a and 16b. Eachof bundles 16a and 16b has an insulating sheath (18a and 18b,respectively) and has an exposed carbon fiber tip at each end. In thepresent embodiment, the sheathed carbon fiber bundles 16a and 16b arehelically wound around the exterior of the stylet guide 14. In thisembodiment, the sheaths 18a and 18b, and stylet tube 14, are made of afluorocarbon material, such as polytetrafluoroethylene (PTFE).

The lead 10 also includes a tip assembly 20 at its distal end whichprovides an exterior electrically conductive surface which is coupled tothe carbon fiber bundles passing within the cover 12. At the proximalend of lead 10, a terminal assembly 22 provides a conductive electricaltermination to the carbon fiber bundles. This termination is suitablefor coupling to conventional electronic sensor or signalling devices,such as an implantable cardiac pacer. In addition, the terminal assembly22 includes a central opening 23 which is coupled to the interior ofstylet tube 14. This opening 23 is particularly adapted for permittingthe insertion of a stylet into the stylet tube 14.

FIGS. 2-5 show the distal end tip assembly 20 and its component parts indetail. More particularly, FIG. 2 show a cutaway view of the tipassembly 20. Assembly 20 includes an electrode 30 (shown in detail inFIGS. 3 and 4) which has a tip portion 32 at one end, a contact portion34, a neck portion 36 interconnecting the contact portion 34 and the tipportion 32 along a central axis 38, and a post portion 44 at its otherend. The post portion 44 extends along the central axis 38 away from thecontact portion 34. In the present embodiment, the neck portion 36 has arelatively small cross-sectional area relative to the adjacent sectionsof the tip 32 and contact portion 34. The contact portion 34 includesthree substantially planar lateral contact surfaces 41, 42 and 43. Inalternate embodiments, differing numbers of contact surfaces may beused. As shown in FIG. 4, the contact portion 34 includes regions 46, 47and 48 which respectively lie between the planar surfaces 41, 42 and 43.

An electrically conductive hollow electrode housing member 50 ispositioned about the contact portion 34 and the post portion 44 of theelectrode 30. Electrode housing member 50 includes a lip 51 at one end.

In the assembled form, the exposed tips of carbon fiber bundles 16a and16b as well as the end stylet tube 14 extend to respective ones of thecontact surfaces 41-43, and beyond to the neck portion 36. The exposedtips are cemented to a respective one of the surfaces 41-43, as well asto the inside surface of housing member 50. The adhesive used forcementing the carbon fiber tips to their respective contact surfaces iselectrically conductive, such as a silver or platinum-loaded epoxymaterial. In addition, the end of housing member 50 is crimped (at 53)to mechanically secure, as well as electrically couple, the carbon fibertips and end of tube 14 to the electrode 30. The crimp 53 of housing 50at neck portion 36 forces the lip 51 of housing 50 to cooperativelyinteract with the post portion 44 to mechanically secure the sheathingfrom the fiber bundles and the tube 14 against electrode 30.

In the present embodiment, a conductive potting 52 is also positionedwithin the housing 50 in contact with electrode 30. In addition, theassembly 20 includes an insulating member 60 which may be of silastic orpolyurethane or other suitable moldable material, which is positionedabout the housing member 50 and overlaps the cover 12 and the neckportion of electrode 30, bonding and moisture sealing the entire tip andlead body assembly.

With this configuration, the exposed tips of the two carbon fiberbundles 16a and 16b are cemented to the contact surfaces of theelectrode 32. The electrically conductive adhesive on tips of bundles16a and 16b, and the crimp coupling at neck 36 provide electricalcontact, as well as mechanical coupling, between the fiber bundles andthe electrode 30. Moreover, the conductive potting 52 within theelectrode housing 50 further insures good electrical contact between thecarbon fiber bundles and the electrode 30. The frictional engagement ofthe housing 50 to the portions 46, 47 and 48 of contact portion 34,together with the potting 52, as well as frictional engagement of tip 51and post 44 with the bundles 16a and 16b insure good mechanical contactbetween the carbon fiber bundles within the cover 12 and the electrodetip 30.

FIGS. 6-10 show the proximal end terminal assembly 22 and its componentparts in detail. More particularly, FIG. 6 shows a cutaway view of theterminal assembly 22. The assembly 22 includes a terminal member 60(shown in detail in FIGS. 7 and 8) which includes two connected hollow,cylindrical ends 62 and 64 which are coaxial about an axis. In thepreferred embodiment, the first end 64 has a relatively small outerdiameter compared with the second end 62. In other forms of theinvention, both ends 62 and 64 may have the same diameter.

In the terminal assembly 22, the ends of sheaths 18a and 18b near theterminal end of 10 are split and the fibers at that end pass through thesplit to form an exposed tip. The first end 64 is positioned about oneend of the stylet tube 14, and the second end 62 is in part positionedabout a portion of the stylet tube 14 as well as portions of the carbonfiber bundles 16a and 16b within their sheaths 18a and 18b,respectively. The terminal member end 62 includes two ports denoted byreference designation 70 and 72. Each of ports 70 and 72 is adapted toguide one of the carbon fiber bundles 16a and 16b from its respectivesplit portion of sheating 18a and 18b from the region interior toterminal member end 62 and to the region exterior to that end 62. Theexposed tips and sheathing are folded back against the outer surface ofend 62, with the fiber bundles outermost.

The terminal assembly 22 further includes an electrically conductivehousing member 80, shown in detail in FIG. 9. The housing member 80 ispositioned about the cylindrical portion 62 so that the inner surface ofhousing 80 sandwiches the exposed tips and associated sheathing betweenthat inner surface and the outer surface of terminal member end 62. Thehousing member 80 may be mechanically coupled, or secured, to terminalmember 60, for example, by a threaded coupling, crimp (particularly inthe region of ports 70 and 72), or spot weld. In some forms of theinvention, an electrically conductive adhesive cements those exposedtips and shething between the housing member 80 and end 62. In alternateembodiments, a conductive potting may be used within housing 80 and end62 to further insure good electrical contact between the carbon fiberbundles and terminal member 60.

The terminal assembly 22 further includes a stylet entry guide member 84having a hollow end portion 88 coupled to a coaxial, hollow body portion90. Guide member 84 is positioned within the terminal member end 64 ofterminal member 60 so that the outer surface of guide member 84frictionally engages the inner surface of end 64. The outer surface ofpart of the body portion 90 is threaded and is frictionally engaged withthe inner surface of the stylet tube 14. In the present embodiment, amolded insulating member 92 is positioned about a portion of thecylindrical portion 64 as well as the housing member 80 and the end ofouter sheathing 12 forming a moisture seal. As shown, member 92 is aseal particularly adapted for use with an implanted cardiac pacemaker.

With this configuration, the exposed tips of the two carbon fiberbundles 16a and 16b are mechanically and electrically coupled to theterminal assembly 22. The electrically conductive adhesive on the tipsof bundles 16a and 16b provides additional mechanical and electricalcontact between the fiber bundles and terminal member 60. The frictionalengagement of the housing 80 to the fiber tips and to the sheathinginsures good mechanical contact between the carbon fiber bundles withinthe cover 12 and the terminal member 60.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

I claim:
 1. A tip assembly for an implantable carbon fiber lead havingan outer cover disposed about a stylet tube and one or more carbon fiberbundles, each of said bundles having an insulating outer sheath andhaving an exposed carbon fiber tip at one end, comprising:A. anelectrode having a tip portion at one end, a contact portion, a neckportion interconnecting said tip and contact portions along a centralaxis, a post portion extending along said central axis from the end ofsaid contact portion opposite to said neck portion, said neck portionhaving a small cross-sectional area relative to adjacent sections ofsaid tip and contact portions, and said contact portion having aplurality of substantially planar lateral contact surfaces, and B. anelectrically conductive, hollow cylindrical electrode housing memberdisposed about said post portion, said contact portion, and at leastpart of said neck portion wherein the interior surface of said electrodehousing member includes a lip at its end nearest said post portion, andwherein said housing member includes a means for biasing said lipagainst said carbon fiber bundles and associated sheathing and said postportion, and for securing said exposed tips between a portion of saidhousing overlying said neck portion and said neck portion.
 2. A tipassembly according to claim 1 wherein said biasing and securing means isa crimp in said housing member.
 3. A tip assembly according to claim 1or 2 further comprising an electrically conductive adhesive means forcementing each of said exposed tips to an associated one of said contactsurfaces.
 4. A tip assembly according to claims 1 or 2 furthercomprising a conductive potting within said housing member.
 5. A tipassembly according to claims 1 or 2 further comprising an insulatingmember disposed about said electrode housing member and said neckportion.
 6. A tip assembly according to claims 1 or 2 wherein said fiberbundle insulating sheath is a fluorocarbon material.